1. Field of the Invention
The present invention relates to pilot injection control of a diesel internal-combustion engine, and particularly relates to pilot injection control that may achieve suppression in torque variation in a transient response of engine rotational frequency.
2. Description of the Related Art
In a diesel internal-combustion engine, pilot injection is performed with multi injection in order to achieve mild combustion and thus reduce engine vibration during combustion, which has been a well-known technique in the past. Furthermore, such pilot multi-injection is effective for preventing misfire at low temperature, or improving fuel consumption. Therefore, the pilot multi-injection is currently widely used as disclosed, for example, in JP-A-2002-269229.
Typically, the pilot multi-injection control includes a method where a plurality of maps are prepared depending on external environment such as ambient temperature so that number of pilot injection is determined using fuel injection amount and engine rotational frequency as parameters, and one of the maps is selected depending on external environment during pilot injection, and number of pilot multi-injection is determined from fuel injection amount and engine rotational frequency at that time.
However, such so-called map control has a drawback that if number of pilot injection is changed in a transient response of engine rotational frequency, which may occur in the case of sudden depression of an accelerator, vibration in engine or variation in torque is induced. While such a drawback has been known in the past, most of pilot multi-injection control techniques are largely focused on reducing engine vibration during combustion, or on preventing misfire in an engine at low temperature. Therefore, a pilot multi-injection control technique giving full consideration to the above drawback is desired.